1. Field of the Invention
The present invention relates to industrial robots and methods of controlling the same.
2. Discussion of the Background
There have been increasing applications of robots with motors to humanoid robots as well as to industrial robots. An exemplary mechanism is disclosed in Japanese Unexamined Patent Application Publication No. 2004-283940, showing a recent trend that a joint shaft is moved by a plurality of motors. Specifically, there is a proposal in which rotation at a single joint is realized with two motors.
In fields to which industrial robots are applied, there is a demand for improved throughput in the conveyance of goods so that productivity is improved. To meet such a demand, the speeds of operations of individual joint shafts included in industrial robots need to be increased, and the responsivenesses of motors therefore need to be improved. To increase the operating speeds, however, the outputs of the motors need to be increased, and the sizes of the motors are therefore increased. Consequently, the inertias of the motors are increased, leading to a problem that the responsivenesses of the motors cannot be improved.
There has been another trend that manufacturing facilities are designed with short manufacturing lines by reducing the footprints of industrial robots so that goods throughput is improved.
In this respect, since the known example employs a robot in which a single shaft is simply rotated by two motors, the two motors need to cooperate. This leads to a problem that the control operation becomes complicated.
Moreover, if a sudden instruction for stop such as emergency stop is issued, operations of the two motors are simultaneously stopped. Therefore, sudden reactive forces act on arms and speed reducers of the industrial robot. In such a case, deterioration of movable parts and relevant components due to aging may be accelerated. From the viewpoint of improving the goods throughput, it problematically takes a long time to perform maintenance work.